Fix #4405: Post version table css doesn't keep ratio at smaller resolutions.

Bug: extremely long sources cause the Tags column to become extremely
wide. Caused by the source link not having the word-break property set.

Fix: use post_source_tag, which lets the `a[rel=external] { word-break: break-word; }`
rule take effect.

Example: https://danbooru.donmai.us/post_versions?search%5Bpost_id%5D=3809742

app/views/modqueue/_post.html.erb

@@ -40,7 +40,7 @@
     <div class="row">
       <span class="info">
         <strong>Source</strong>
-        <%= post_source_tag(post) %>
+        <%= post_source_tag(post.source, post.normalized_source) %>
       </span>
     </div>